A color cathode ray tube of shadow mask type is formed such that electron beams emitted from an electron gun having R red, G green, B blue beam holes pass through apertures of the shadow mask to land on R, G, B phosphorescent layers.
However, a part of the electron beams pass through the apertures of the shadow mask but a part of them strike the shadow mask to heat its face, so that the thermal expansion occurs in the face of the shadow mask to dome out. Such doming results in the changing of the aperture position against the electron beam, so that such doming should be corrected.
A conventional method for solving the doming of the shadow mask is such that a bimetal spring which is called a hook spring is interposed between a stud pin installed at a predetermined position of the inner surface of a face panel and the shadow mask frame suspended from it to compensate for the changing of the aperture position caused by the shadow mask doming.
The bimetal spring is installed at the middle part or the edge of the shadow mask frame. The structure of the bimetal spring's installation at the edge of the shadow mask frame has an advantage such that the bimetal spring holds back the free vibrations of the shadow mask frame.
The method such as described above is disclosed in the U.S. Pat. Nos. 3,894,260, 3,935,496, 3,921,024 and 3,986,071. A suspending system of such inventions has a clamping member attached to the edge of the shadow mask frame in common. The clamping member is provided with a pair of tension arms and bimetal springs to be welded to a predetermined position of the shadow mask frame or connected to the shadow mask frame by a locking member.
Such a suspending system results in an increased number of elements and its complex structure results in the difficultly attaching and detaching. Thus, as is the case during the manufacturing process of the color cathode ray tube, the attaching and detaching operation of the face plate and shadow mask frame is repeated many times, the elements can be easily deformed.
In particular, assembly of the structure disclosed in U.S. Pat. No. 3,894,260 can not be formed by using manufacturing equipment of the conventional color cathode ray tube since stud members for supporting the one end of the bimetal spring should be installed at all edges.
Also, in the case of the face plates disclosed in U.S. Pat. Nos. 3,921,024 and 3,935,496, because such face plate have a recess at all edges where the bimetal spring can be set, a metal mold for a new face plate should be used.
U.S. Pat. No. 3,986,071 has a disadvantage such that, whereas a pair of stud pins are installed at the edge of the face plate to support the both ends of the bimetal spring, the system of such method results in an unstable suspending state of the bimetal spring.
The simplest structure of the bimetal spring supporting the corner part of the shadow mask frame is described in FIG. 3. The bimetal spring 2 shown in FIG. 3 has a fixing plate 8 attached to the edge of the rigid frame 6 supporting the shadow mask and a supporting plate 10 of which one end is united to the fixing plate 8.
The supporting plate 10 has a hole 16 which is penetrated and supported by the stud pin 14 of the face plate 12. The above suspending system has disadvantage such that, during the attaching and detaching operation which is repeated many times in the manufacturing process, the suspending system is folded in the direction of arrow X, so that the elastic coefficient of the supporting plate 10 is easily changed.
In addition, when the frame 6 is shaken by the impact applied from the outside according as the weight of the frame 6 is connected on the supporting plate 10, the supporting plate 10 twists against the fixing plate in the direction of arrow Y.